1. Field of the Invention
The present invention relates to a control unit for controlling the operation of a load and to a flame scanner control unit for reducing the noise content of a voltage signal which is representative of the intensity of a monitored flame.
2. Description of the Prior Art
During the operation of industrial and utility boilers it is critical that the supply of fuel to the flame in the boiler be stopped when the flame goes out. Should the supply of fuel continue after the flame is out, there is a potential for a combustion explosion due to the flame re-igniting or other flames in the boiler igniting the excess fuel. There is also a potential for steam to build up within the boiler resulting in a steam explosion.
Flame scanning systems have been developed for the purpose of reducing the risk of explosions in boilers due to the flame going out. The flame scanning system commonly includes a scanner which monitors a flame in the boiler and provides a signal indicating whether or not the monitored flame is present. The flame scanning control system further includes a relay switch that is connected in series relation with the control circuitry of a fuel valve. In the event the flame scanner sees that the flame has gone out, the flame scanner sends a signal to the relay switch control causing the relay to open circuit or de-energize the fuel valve control circuitry. When the valve control circuitry de-energizes the fuel valve closes thereby impeding the flow of fuel to the boiler. The present relay switch utilized in a flame scanning system comprises a relay switch whose control circuitry is driven by a driving transistor. The driving transistor is responsive to a flame on signal received from the flame scanner.
One problem associated with the above flame scanning system occurs when the contacts of the relay switch weld and do not break the circuit controlling the operation of the fuel valve. Consequently there is a potential for an explosion in the boiler.
Another problem associated with the flame scanning system resides in the driving transistor used to control the operation of the relay. When the relay de-energizes, an excess amount of voltage may cause the transistor driver to fail in a short circuit mode. As a result, when the driving transistor receives a flame off signal from the flame scanner, the driving transistor cannot de-energize the relay to break the circuit controlling the fuel valve.
Another problem inherent in the present flame scanning system is the flame scanner may not be able to discriminate between the flame it is mohitoring and other flames in the boiler. Accordingly, the flame scanner may not provide the necessary signal when the monitored flame goes out. While the optics in the flame scanner have been adjusted to reduce the focus of the flame scanner to a small area, this is not satisfactory.